Washington: Air defence forces were put on high alert and cities across the US increased security after Wednesday's deadly shooting attacks on the Canadian parliament in the capital city of Ottawa.

Shortly after the attack, President Barack Obama spoke to Canada's Prime Minister Stephen Harper on the phone and offered any assistance Canada needed in responding to these attacks, the White House said in a statement.

Condemning the shootings as "outrageous acts," Obama said, "We're all shaken by it." As more becomes known about the shooter's motive, that information will be factored into US security considerations, he said. "We have to remain vigilant,"

"It's very important, I think, for us to recognize that when it comes to dealing with terrorist activity, Canada and the United States has to be entirely in sync," Obama told pool reporters in the afternoon.

Secretary of State John Kerry was also briefed on the shootings, according to State Department spokesperson Mary Harf.

One soldier who was shot at Canada's National War memorial, located across from the Parliament building, has died, according to CNN. The gunman was shot and killed on the scene inside Parliament Hill's Centre Block.

Meanwhile, in the midst of heightened security, a man jumped over the White House fence on Wednesday night. But unlike a previous jumper, he barely made it onto the lawn before being taken down by two police dogs and quickly detained by Secret Service agents.

In mid-September, another man made it into the White House before being detained.

North American Aerospace Defense Command (NORAD), which provides air defence over North America, is increasing its alert posture and the number of planes ready to respond to a problem, CNN reported.

It's also in continuous contact with Canadian law enforcement.

"We have taken appropriate measure to ensure that NORAD is postured to respond quickly if the ongoing situation in Ottawa should include any effect on aviation," NORAD spokesman Captain Jeff Davis was capitol was quoted as saying.

At the US Capitol, which was the site of a deadly shooting in 1998, police are "monitoring and tracking" developments in Canada.

But as of now, they haven't modified their regular "post 9-11 heightened state of alertness," CNN said citing US Capitol Police spokeswoman Kim Schneider.

Congress is on recess until next month's elections, though the Capitol remains busy with tourists, staff and other workers.

Across the Potomac River, security near Arlington Cemetery has increased, specifically at the Tomb of the Unknown Soldier.

The US Embassy in Ottawa, located near the Ottawa River next to Parliament Hill, is on lockdown, CNN said citing a message posted on Twitter.

In New York City, the Police Department has added extra security to the Canadian consulate as a precaution, CNN reported.

Meanwhile, reporting from Ottawa, CBS News cited law enforcement and US Government sources as saying the suspect was Michael Abdul Zehaf Bibeau, born in Canada in 1982.

Bibeau was reportedly shot to death by the ceremonial sergeant-at-arms of the House of Commons, a former police officer. The gunman's motives have not been determined, it said.

"This week's events are a grim reminder that Canada is not immune to the types of terrorist attacks we have seen elsewhere," Harper said in a national address. But "We will not be intimidated. Canada will never be intimidated."